Focusing on the characteristics of selfishness of relay users and asymmetric network information in cognitive radio networks, a multi-user cooperative communication mechanism was proposed. Firstly, by modeling the cooperative communication as a labor market, a modeling method for the multi-user contract-based relay selection framework was investigated under the symmetric network information scenario. Then, to avoid the adverse selection problem due to the hidden-information of Secondary User (SU) before contract assignment, a contract-based relay selection model was proposed to incentivize the contribution of secondary users for ensuring cooperative communication. The experimental results show that, by hiring the secondary users with better channel condition or less relay cost, Primary User (PU) can obtain much more cooperative communication utility. The proposed multi-user contract-based cooperative communication framework can put forward new ideas for efficient utilization of spectrum resource.

To alleviate the shortage of licensed spectrum resource, a method to design and implement the multi-user Cooperative Spectrum Sharing (CSS) mechanism was proposed based on the characteristics of asymmetric network information and selfishness of communication users. First, by modeling the CSS as a labor market, a modeling method for the multi-user contract-based CSS framework was investigated under the symmetric network information scenario. Then, to avoid the moral hazard problem due to the hidden-action of Secondary Users (SUs) after contract assignment, a contract-based CSS model was proposed to incentivize the contribution of SUs for ensuring spectrum sharing. The experimental results show that, when the direct transmission rate of Primary User (PU) is less than 0.2 b/s, in comparison with the case of non-cooperative spectrum sharing, the capacity of network is more than 3 times larger. The proposed multi-user contract-based CSS framework will put forward new ideas for efficient sharing and utilization of spectrum resource.

Concerning the poor positioning rate and localization precision of Grid-Scan algorithm, an improved Grid-Scan localization algorithm based on virtual beacon nodes was proposed. Three related works were mentioned as follows: Firstly, the unknown nodes which have neighbor beacon nodes located themselves by using the beacon nodes, and the located unknown nodes were upgraded to virtual beacon nodes. Secondly, the unknown nodes that do not have neighbor beacon nodes got their location through virtual beacon nodes. Finally, different communication radiuses were set between beacon nodes, virtual beacon nodes and unknown nodes to scan in order to accomplish the localization. The simulation results show that the improved algorithm’s positioning accuracy and positioning rate increase by 6.35% and 23.37% on average respectively.

According to the nonlinear and non-stationary dynamic characteristics of the network traffic, the technique based on synergetic phase transition theory was proposed for detecting network traffic anomalies. By using the nonlinear dynamic equation of the order parameter, the paper described the complex behaviors of the network traffic system in discrete wavelet domain of the network traffic time series and the potential function was used to characterize non-stationary phase transition process of the network traffic system. The relationship between network traffic status and the various attack patterns was analyzed, and the synergetic model was used to calculate the network traffic order parameter. When the corresponding order parameter converged, the corresponding attack pattern or the normal traffic pattern could be detected. Finally, the DARPA 1999 data set was used to evaluate the proposed method. The average detection rate is 90.00% and the average false alarm rate is 15.03%. The experimental results show that the proposed method is effective for the network traffic anomaly detection.

Focusing on the problems of poor locating performance and ignoring anchor nodes' inaccuracy in traditional DV-Hop algorithm which is one of the range-free algorithms in Wireless Sensor Network (WSN), an intelligent algorithm for locating nodes based on Processing Strategy of Optimal Hopping Distances (PSOHD) was proposed. Fully considering the effect of dynamic topology and anchor nodes' difference, this algorithm firstly introduced two communication radii with anchor nodes to calculate the nodes of communication range respectively. Secondly, the average one-hop distance among anchor nodes was refined by means of weighted least squares estimation. Finally, the average one-hop distance used by each locating node for estimating its location was optimized through weighting the N received average one-hop distances from anchor nodes. In addition, Particle Swarm Optimization (PSO) algorithm was presented to locate the unknown nodes. The simulation results show that the improved algorithm has obviously better location precision at the cost of increasing appropriate energy. Thus, it is a practical scheme for WSN with both inaccuracy of anchor nodes and random dynamic topology.

With the aim of overcoming the encoding complexity, a novel and fast neighbor codeword search algorithm for vector quantization in the Handamard transform domain was presented. In the proposed algorithm, firstly the Hadamard transform was applied to all the codewords in the codebook and the input vector. Then the initial match codeword was selected from the codeword whose norm was nearest to the norm of input vector on Hadamard transform. Furthermore, the triangle inequalities with multiple control vectors and the two elimination criteria were utilized to reject mismatch codewords. Finally, the best-match codeword to the input vector was found. Experimental results show that the proposed algorithm has greatly reduced codeword search time and computational complexity under the precondition of good restored image quality.

To overcome a variety of attacks, a novel solution was proposed. The solution is to establish a trusted relation between all neighboring nodes while avoiding untrustworthy nodes during the route discovery process so as to resist DoS-style flooding attacks. This scheme was described in detail. The extensive simulation results indicate clearly that this scheme can resist DoS in wireless sensor network, and its additional overhead is reasonably low.